As the microprocessor finds increasingly wider applications in controlling systems, the need for reliable and low cost sensors and transducers for interfacing between the microprocessor and the system to be controlled has grown rapidly. One such example is the application of microcomputers for controlling automobile engines. An overview of such an application may be found in "Automotive Electronics II: The Microprocessor Is In" by Puckett et al, IEEE Spectrum, Vol. 14, No. 11, November 1977. This article calls attention to the current unavailability of efficient, low cost sensors and transducers.
Desirable features of a temperature sensor circuit include suitability for implementation with monolithic integrated circuit technology, implementation with a relatively small number of components, insensitivity to process variations from wafer to wafer, and insensitivity to variations in the power supply voltage applied to the temperature sensing circuit. The analog output signal should vary linearly with temperature in order to allow for conventional analog-to-digital conversion techniques. In addition, a differential output signal is a desired feature when the temperature sensor is to be used in a high noise environment in order to benefit from the advantages of common mode noise rejection. It will be appreciated by those skilled in the art that a temperature sensor circuit which includes all of the desired features mentioned above is a significant improvement over the prior art.